1. Field of the Invention
The present invention relates to a thin-film magnetic head with a heating element and a heatsink, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic disk drive apparatus with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, when writing or reading signals, a thin-film magnetic head (slider) hydrodynamically flies with a predetermined spacing (flying height) on a rotating magnetic disk. While flying on the magnetic disk, the thin-film magnetic head writes signals to the magnetic disk using magnetic fields generated from an inductive write head element, and reads signals by sensing magnetic fields corresponding to the signals from the magnetic disk with the use of an magnetoresistive (MR) effect read head element. On these cases, a magnetic spacing do is defined as an effective magnetic distance between ends of these head elements and the surface of the magnetic disk.
With higher recording density due to the increase in data storage capacity and miniaturization of the magnetic disk drive apparatus in recent years, a track width of the thin-film magnetic head is becoming smaller. In order to avoid the degradation of writing and reading performance due to the smaller track width, latest magnetic disk drive apparatus actually has the magnetic spacing dMS reduced down to the order of 10 nm or less.
Generally, when write currents are applied to the inductive write head element, a thermal pole tip protrusion (TPTP) phenomenon occurs due to a thermal expansion by Joule heat, eddy-current loss and so on, where the end of the magnetic head element is protruded toward the surface of the magnetic disk. In the case, the much small magnetic spacing dMS is likely to cause the protruded end of the magnetic head element to contact the surface of the magnetic disk. The contact by the protrusion has a possibility of making trouble (thermal asperity) such as an occurrence of abnormal signals, and further has a risk of causing physical damage or crash of the magnetic head element and the magnetic disk.
To avoid the troublemaking contact, some techniques are proposed, which control the magnetic spacing dMS by positively utilizing a TPTP phenomenon with the use of a heater provided inside the thin-film magnetic head, for example, in U.S. Pat. No. 5,991,113, US Patent Publications Nos. 2003/0174430 A1 and 2003/0099054 A1. In these techniques, the magnetic spacing dMS is designed in prospect of a protrusion due to the heat generated from the heater, and is adjusted by controlling the power applied to the heater during operation.
When the heater is provided in an overcoat layer covering the magnetic head element and in a position being in a certain distance from the slider substrate, the heat generated from the heater is accumulated in the overcoat layer, and causes the effective thermal expansion of the overcoat layer. As a result, the whole amount of protrusion of the head end surface per applied power becomes larger. However, in order to protrude the end of the magnetic head element effectively, the heater is needed to be closer to the magnetic head element. In the closer position, the heater also becomes closer to the slider substrate with comparatively high thermal conductivity. Therefore, the closer position of the heater causes the heat generated from the heater to be more dissipated via the slider substrate. As a method for avoiding this dissipation, the heat may be concentrated to the magnetic head element by miniaturizing the heater. The miniaturization of the heater enables the end of the magnetic head element to be protruded more effectively.
However, the miniaturization of the heater is likely to cause the temperature of the heater itself to be increased excessively. Generally, a stable heating operation even under intermittent uses is required to control the much small amount of the protrusion. Therefore, the heater is needed to have a high-precision in position and size, however, the excess increase in temperature has a possibility to cause the heater to be deformed, and what is more, to be destroyed due to breaking and so on. Therefore, in the case of the excess increase in temperature, not only the required degree of precision, but also the heating operation itself is not assured.
To deal with the problem, a thin-film magnetic head described in US Patent Publication No. 2004/0017638 A1 has a heatsink layer for diffusing the heat generated from the inductive write head element, though having no heater. In this head, the excess increase in temperature of the heater may be prevented, for example, by providing the heater near the heatsink to diffuse the heat accumulated in the heater itself. Furthermore, a thin-film magnetic head in which a heater is provided in a position above and opposed to a lower core layer (lower magnetic pole layer) though not for the purpose of diffusing heat, is disclosed in Japanese patent Publication No. 2005-011414A. The excess increase in temperature of the heater may also be prevented in this head.
However, a problem occurs that the heat generated from the heater is likely to degrade the reliability of the MR read head element.
When using either above-mentioned thin-film magnetic head described in US Patent Publication No. 2004/0017638 A1 or Japanese patent Publication No. 2005-011414A, the heat generated from the heater is likely to cause the temperature of an MR multilayer, which is a sensing part of the MR read head element, to be significantly increased because the large amount of the heat reaches the MR read head element through the heatsink layer or the lower magnetic pole layer. The significant increase in temperature is likely to cause deterioration in the reliability, and what is more, the output stability of the MR read head element. Especially, a giant magnetoresistive (GMR) read head element, which is recently well-used, has a comparatively high risk to make such a problem.